Start by checking your fuse's for the headlight's then check the power wire to the dim headlight and see if it read's full battery voltage with the headlight on compare the voltage to the bright one. If all that is good use a ohm's to check the ground going to the headlight and see if you 2 ohm's or less to the dim headlight. Checking all of those thing's you should find the answer why the headlight is dimmer then the other one.
February, 9, 2014 AT 11:48 AM
Yabuddy when my one headlight was dim it was a bad headlight ground it was making my car stahl when I had my lights on when I would hit my horn or my right turn signal it was a bad ground it kept saying malfunction headlights
And that was on my benz e430 4matic